A huge market exists for disk drives for mass-market computing devices such as desktop computers and laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g. personal digital assistants (PDAs), cell-phones, digital cameras, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Disk drives typically employ a moveable head actuator to frequently access large amounts of data stored on a disk. One example of a disk drive is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the moveable transducer head over a particular track on the disk to read or write information from and to that track, respectively.
Typically, a conventional hard disk drive includes one or more disks wherein each disk includes a plurality of concentric tracks. Each surface of each disk conventionally contains a plurality of concentric data tracks angularly divided into a plurality of data sectors. In addition, special servo information may be provided on each disk to determine the position of the moveable transducer head.
The transducer head typically includes a reader and writer for reading and/or writing data from and to the disk, respectively. The transducer head is typically mounted on a head carrier. The head carrier is commonly an air-bearing slider attached to an actuator arm by a suspension and is positioned very close to the disk surface by the suspension.
The spacing between the head and the disk surface is called the flying height. The slider typically has a disk-facing air-bearing surface (ABS) that causes the slider to ride on a cushion or bearing of air generated by the rotation of the disk. The slider is typically attached to a flexure on the suspension and the suspension includes a load beam that applies a load force to the slider to counteract the air-bearing force while permitting the slider to “pitch” and “roll”. The flying dynamics of the slider and thus the flying height of the head are influenced by factors such as rotation speed of the disk, the aerodynamic shape of the slider's ABS, the load force applied to the slider by the suspension, and the pitch and roll torques applied to the slider by the suspension.
Disk drives may utilize a flying height actuator for changing the spacing between the head and the disk surface. One type of flying height actuator utilizes a thermal actuator with an electrically-resistive heater located on the slider near the head. When current is applied to the heater, the heater expands and causes the head to “protrude” such that it moves closer to the disk surface. The flying height actuator should be accurately calibrated so that the head-disk spacing can be controlled. The calibration often requires that the value of the control signal that results in the onset of head-disk contact (HDC) be known.
Presently, during disk drive manufacturing, a head-disk touchdown calibration value is determined by applying a dynamic flying height (DFH) voltage to the head until a touchdown detection occurs. The DFH voltage is typically applied by a flying height actuator (FHA). The DFH voltage is typically square-waved such that its profile consists of an instant rise of voltage at a leading end, constant voltage applied over at least one revolution, and an instant falling voltage at a trailing end.
Unfortunately, the square-waved DFH voltage often causes head instability during touchdown detection. The head instability often results in false touchdown detection followed by incorrect preamplifier settings or undesirable head-disk interaction which causes carbon wear on the slider surface and lubricant degradation on the disk media surface.
Therefore, there is a need in the disk drive manufacturing process to better apply DFH voltage to prevent head instability and to improve touchdown detection.